Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-05-31
2003-01-14
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109400, C430S111400
Reexamination Certificate
active
06506530
ABSTRACT:
This application is based on application No.156508/1999 and No. 132310/2000 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color toner for developing electrostatic image suitably used in full color image-forming apparatuses such as a full color electrostatic copying machine, a full color laser beam printer and the like.
2. Description of the Related Art
In a full color image-forming method in electrophotography, the most significant properties required for toners were to have sharply melting properties so that toner layers of various colors are instantaneously melted by heat, mixed and develop color in a fixing process in order to form full color images by laminating toner images of a magenta toner, a cyan toner, an yellow toner and a black toner (U.S. Pat. Nos. 4,142,882, 4,590,139 etc.). However, such toners had high viscosity, extremely low elasticity, and small intermolecular coagulation force when toners melted by heat, causing a problem of offset onto a heat roller (particularly, offset at higher temperatures). Such a problem was remarkable, particularly when a roller is deteriorated due to repeated use, and when images such as full color images (for example, photographic image) having a large toner-adhered area and having a large toner amount on a toner support member (such as paper and the like) are copied.
On the other hand, with the prevalence of color printers and copying machines having high image quality, the number of sheet with copied color images increases dramatically. Further high speed is required. Under such recent conditions, toners giving small change of image gloss in continuous copying are in need. If change of image gloss is significant, appearances, namely, color and color reproducibility are felt significantly different by person.
However, when a conventional toner of which sharply melting properties are emphasized is used, there is a problem that image gloss changes significantly in continuous copying. Speedup of copying makes this problem more remarkable. Such a gloss change is believed to be derived from lowering of fixing roller temperature due to gradual deprivation of heat on the surface of the fixing roller by paper. Further, when continuous copying is conducted using A4 paper at longitudinal direction before copying using A4 paper at transverse direction, different gloss occurs on one sheet of image paper. This is problematical. In more detail, when A4 paper is used at longitudinal direction, both end portions of a fixing roller are not used for fixing, whereas, when A4 paper is used in transverse direction, both end portions of a fixing roller are also used for fixing as well as center portions. Therefore, temperature difference between the center portions and both end portions of a fixing roller occurs in copying in longitudinal direction of A4 paper, and when copying is conducted at transverse direction of A4 paper, high gloss portions and low gloss portions appear on one sheet of copied images. The problems of gloss change (difference) by continuous copying and gloss change (difference) on one sheet of copied images (hereinafter, simply referred to as “gloss change”) are particularly remarkable in cold regions and after switch on.
U.S. Pat. No. 4,657,837 and G.B. No.2,100,837 propose a technology in which a polyester composed of an etherified bisphenol monomer and a divalent carboxylic acid monomer is cross-linked with a large amount of not less than tri-valent alcohol monomer and/or a not less than tri-valent carboxylic acid monomer, to give a polyester which is used as a binder resin. A toner obtained by using this binder resin can suppress offset at higher temperature and gloss change with change of fixing temperature. However, due to poor sharply-melting properties, the toner can not be fixed at lower temperature and color developing properties becomes problematical (lower temperature fixing properties).
Japanese Patent Application Laid-Open No. 60-67,958 proposes a technology in which two kinds of resins, or a non-linear polyester and linear polyester are so blended that the amount of the non-linear polyester is dominant. As a result of investigations of this binder resin by the present inventors, it is known that though offset at higher temperature and change of gloss with change of fixing temperature can be suppressed to a certain extent, the desired fixing properties at lower temperature can not be achieved.
SUMMARY OF THE INVENTION
The present invention is to provide a color toner for developing electrostatic images, which can suppress gloss change with change of fixing temperature, and is excellent in offset-resistance and fixing properties at lower temperature.
The present invention relates to a toner comprising:
a coloring agent;
a binder resin comprising a first binder resin and a second binder resin, the first binder resin being composed of a linear polyester resin having a number-average molecular weight (Mn) of from 2,800 to 7,000, a weight-average molecular weight (Mw) of from 8,900 to 21,000, and a Mw/Mn ratio of 2 to 4, the second binder resin being composed of a non-linear polyester resin having a number-average molecular weight (Mn) of from 3,500 to 8,000, a weight-average molecular weight (Mw) of from 40,000 to 120,000, and a Mw/Mn ratio of 10 to 20, and a ratio of the first binder resin to the second binder resin (the first binder resin:the second binder resin) being 60:40 to 95:5 by weight.
DETAILED DESCRIPTION OF THE INVENTION
The toner of the present invention comprises, at least, a binder resin, and a coloring agent, and uses two kinds of resins having different molecular weight (first binder resin; lower molecular weight, second binder resin; higher molecular weight,) as the binder resin.
The first binder resin is a linear polyester having a number-average molecular weight (in this specification, referred to as Mn) from 2,800 to 7,000, preferably from 3,000 to 6,000, a weight-average molecular weight (in this specification, referred to as Mw) from 8,900 to 21,000, preferably from 9,000 to 20,000, and a Mw/Mn ratio from 2.0 to 4.0, preferably from 2.1 to 3.5.
In the first binder resin, when Mn is less than 2,800 or Mw is less than 8,900, an effect for suppressing gloss change against change of fixing temperature is not obtained, and en effect to prevent offset at higher temperatures is not obtained. Further, lowering of Tg is caused, and toner storing properties (blocking-resistance) under high temperature deteriorates, in addition, the resin becomes too fragile, and in stirring in a developing vessel, a toner becomes a fine particles, deteriorating durability. When Mn is over 7,000 or Mw is over 21,000, heat-melting properties is inferior, fixing strength at relatively lower temperatures becomes weak, in addition, an image having appropriate gloss can not be obtained at relatively lower fixing temperatures. Further, resin becomes too hard, and pulverizing properties in producing a toner deteriorates. When Mw/Mn is lower than 2, the molecular weight distribution is too narrow, causing offset at higher temperatures in fixing. When Mw/Mn is over 4.0, fixing strength at relatively lower temperatures becomes weaker, in addition, an image having appropriate gloss can not be obtained at relatively lower fixing temperatures. Further, sharply melting properties decreases, the translucency and color-mixing properties of a toner decrease in the fixed image, the reproducibility of color deteriorates, and an excellent full color image can not be obtained. Further, by using a linear polyester as the first binder resin, the first binder resin can have sharply melting properties, and fixing properties at lower temperature when two kinds of resins are blended can be maintained. The linear polyester means a linear polyester having no branched chain.
In the present specification, the number-average molecular weight (Mn) and the weight-average molecular weight (Mw) of a resin are values measured by using gel perme
Aoki Megumi
Arai Takeshi
Hagi Masayuki
Kido Kenichi
Mikuriya Yoshihiro
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
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